Are DEXA scans definitive for developing runners?

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If you have followed me on social media for the last few years, you have probably found that I have a particular interest in stress fractures. Rehabbing runners withs stress fractures, educating others about their development, and reducing their occurrence are some of my main focuses with the patients and athletes I work with. Aside from analyzing training volume, workout intensity, strength training regimen, and a host of other factors, one thing we need to consider is the overall bone health of the individuals we work with. We want to know how strong and resilient someone’s bones are before we figure out how to get them back to running or decrease their risk of a developing a bone stress injury in the future.

A common test used to assess an endurance athlete’s bone health is a DEXA scan. A DEXA (DXA) scan takes a picture of someone’s skeleton and helps establish someone’s bone mineral density (BMD). They can be very helpful in adult populations to see if someone has developed osteoporosis, a bone disease where someone’s bones have become weak and brittle. Marni Sumbal recently wrote a very thorough post on what all they can tell us HERE.

In the endurance world, DXA scans are often performed on athletes with higher risk stress fractures or if they have a history of multiple stress fractures. The idea is to determine if someone’s actual bony integrity is playing a factor into their injuries. While these scans can give us crucial information when someone’s BMD is low, having a normal DXA scan does not necessarily mean that a young runner’s bone health is where we want it to be.

Bone mass (BMD) is a measurement of the amount of calcium and other minerals in our bones. The amount of bone mass present in an athlete can play major role in injury development. A lot of this is determined by genetics, but it can also be influenced by what sports and activities we participate in. Peak bone mass generally occurs for women between the 33 and 40 and 19 and 33 for men (Langenconck 2003). This peak in bone mass generally occurs around seven years after peak height velocity (Baxter-Jones 2011). 

Petit et al wrote a fantastic article critiquing the use of DXA scans in the developing skeleton. You can read it HERE. According to Petit , “bone densitometry methods which have relatively straight forward application in adult osteoporosis, are far more difficult to evaluate in the growing skeleton.” Because DXA scores are based off a ratio, and the inherent nature of growing bone is constantly changing the ratio, we can get a lot of false negatives.

Basically, DEXA scans do not consider the size of bones. Petit also goes on to state, “it does not allow assessments of architecture and geometry.” DXA scans can tell us how much bone is there, but it can’t tell us whether is set up in a good position to deal with the demands of running. He also concluded “it may not be possible to reliably measure the properties of property behavior, especially in 3-d bones.”

The reason I think this is important is because of the number of runners I have seen with “normal” DEXA scans and have an extensive history of bone stress injuries. Certainly things like training volume, recovery, etc. play large roles in BSI development, but simply having a normal DXA scan should not mean we not thoroughly investigate nutritional advice, specific strength training interventions, and all the other factors that can influence bone health. We need more information than a DXA scan can give us.

HOW SHOULD WE DETERMINE AN ATHLETE’S BONE STRENGTH?

Bone strength is generally defined as the amount of loading force required to cause the material to fail under a certain load. In physical therapy school, we learned this as the stress-strain curve (IMAGE BELOW)

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Think about taking a piece of uncooked spagetthi and snapping it in half. As you begin bending the piece of pasta, there is a certain range where if you stopped it would go back to normal (this is the area up to the “yield stress” on the graph). At some point, if you continue to bend the noodle it will either break or be unable to return to the normal range (this is the UTS region on the graph). This how we generally define how strong a bone is, but this fails to represent how three dimensional forces are applied to the human skeleton. 

Petit’s article tells us that using DXA scans as a clearing examines for bone health is too simplistic. Petit states, “To adequately evaluate bone strength in children, we would ideally want to incorporate components of bone strength from the material level, the tissue level, and the whole bone level.”

Petit et al 2015

Petit et al 2015

Material Level Properties

The yield stress is the stress at which a material begins to deform plastically. It is unable to return to it’s original state. That is what we are looking at when we discuss material level properties. Going back to our spaghetti example, this would be the point were it can not completely return to its “unbent” form. The yield stress of bone depends primarily on the properties and orientation of collagen fibers making up the organic matrix and on the mineralization (the degrees the matrix spaces are filled in the inorganic mineral). Certain collagen anomalies reduce the material strength of bone tissue and rapid changes in normal growth produce deficits in mineralization. This highlights the importance of understanding the physical characteristics os someone’s bone as we are evaluating their overall bone health. Currently, we can only do this by invasive means like a bone biopsy. We have to physically assess the bone to determine it’s makeup.

Tissue Level Properties

At the tissue level, we divide bone into trabecular (cancellous) and cortical (compact) bone. In trabecular bone 10-35% is mineralized (filled in) and cortical bone is around 90% mineralized. We want to know how much of something occurs in an individuals bone, but we also want to know how that is oriented. These tissue level properties are best assessed with a CT scan.

Whole Bone Level Properties

To evaluate the “whole bone” we assess BMD. This is where DXA scans can be helpful. BMD is based off a formula and the developing skeleton is constantly changing both in the length of the lever arms (i.e. longer bones), as well as the distribution of cortical vs trabecular bone. For practical purposes, the section modulus (bending strength) and bone cross-sectional area (compression or axial) should be the primary geometric strength outcome parameters 

You would need to know all three of those variables to appropriately determine someone’s bone strength. That’s a lot of radiation, money and stress for either a healthy or injured runner. It would be absolutely unnecessary and impractical to do that with every athlete.

Are there times when someone might need to go through all of that? Yes. The point of this post is to say just because someone has a normal DXA scan does not mean that their bone health is not a factor in their current stress fracture or their future development of bone stress injuries.

If I have an young runner with a normal DXA scan, three previous high risk fractures, has lots of menstrual irregularities, and only swam growing up, I’m much more likely to consider their bone health might not be ideal even if their scan comes back normal.

PRACTICAL APPLICATION

So what can we actually do without running our patients and clients through a million diagnostic tests? Take them through a thorough training and medical history. Here are a few key areas that are MUSTS for discussion with runners.

Past Injury History

Like all injuries, previous injury is the biggest risk factor for a future future injury. If a runner consults me with a history of even one bone stress injury, I have to consider bone health when developing their rehab or training. You need to find out not only if someone has suffered a bone stress injury but also where any BSIs occurred and what the treatment was for that specific injury.

Youth Athletic Experience

Were you active during the years around your biggest growth spurt? Were you participating in sports with high impacts and odd impacts? This can be sports like soccer, basketball, baseball, gymnastics, etc. You are looking for sports that require accelerations, decelerations, jumping and other various loading strategies that runners and endurance athletes don’t experience. These type of loading strategies help the developing bone become more robust than the typical loads applied in endurance sports.

Menstrual History

Menstrual changes are not only an indicator of bone health, but they are also an independent risk factor for ANY running related injury. Arashben and colleagues found that women who exercise and maintain normal menstrual cycles seem to have a higher BMD than amenorrheic women. Rauh et al oligomenorrhea and amenorrhea have also been associated with running related injuries in general, not just BSIs.

Previous Medication Usage

Warden et al in 2014 developed a fantastic study looking at all the factors playing into bone stress injuries. You can read the full text HERE. One thing we have to assess is has someone taken any medications that may influence bone health. A few medications you should be asking about. Corticosteroids, anticonvulsants, antacids, and hormonal supplementation

Past Medical History

Have you had other systemic health concerns that could be playing into bone health? This could be autoimmune disorders, rheumatic disorders, or anything else that systematically effects someone’s health.  

A full understanding of someone’s situation helps us determine their training progression, volume, intensity, strength training regimen, referral to other resources and a host of other decisions to put them in the best situation to succeed.

All of this boils down to communication and a thorough history. Truly developing a relationship and an understanding of an individual can be more helpful then any one diagnostic test. Whether you are a coach, trainer, or medical provider, investigating an individual’s past is vital in order to help them achieve their future goals.

Thanks for reading!

Nathan Carlson PT, DPT

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References:

Petit M, Beck T and Kontulainen S. Examining the developing bone: What do we measure and how do we do it? Musculoskelet Neuronal Interact 2005; 5(3):213-224 2015.

Warden S, Davis I and Fredericson M. Management and Prevention of Bonse Stress Injuries in Long-Distance Runners. Orthop Sports Phys Ther 2014;44(10):749-765. Epub 7 August 2014. doi:10.2519/jospt.2014.5334

Baxter-Jones A, Faulkner R, Forwood M et al. Bone mineral accrual from 8 to 30 years of age: An estimation of peak bone mass. Journal of Bone and Mineral Research, Vol. 26, No. 8, August 2011, pp 1729–1739

Langendonck L, Lefevre J, Claessens A et al. Influence of Participation in High-Impact Sports during Adolescence and Adulthood on Bone Mineral Density in Middle-aged Men: A 27-Year Follow-up Study Am J Epidemiol 2003;158:525–533

Kraus E, Tenforde A, Nattiv A et al. Bone stress injuries in male distance runners: higher modified Female Athlete Triad Cumulative Risk Assessment scores predict increased rates of injury. Kraus E, et al. Br J Sports Med 2018;0:1–7. doi:10.1136/bjsports-2018-099861